The invention concerns a lancet assembly, and more particularly concerns an automatically retractable non-reusable lancet assembly.
Sharp pointed or blade-like lancets, as they are generally known in the art, are employed to make a quick puncture or penetration of the skin of a patient to cause a small flow of blood. Various tests require a relatively small amount of blood, for example a drop smeared upon a slide or the like for microscopic viewing, such that the amount of blood flowing from a finger prick of this type is normally sufficient. Also, various bleeding time tests are often employed in which the time running from the puncture of the skin until the cessation of blood flow is measured. Such bleeding time provides a measure from which, by reference to tables or the like, the clotting factors and/or other such relevant information concerning a patient's blood chemistry can be estimated. One such bleeding time test, referred to in the art as the Ivy technique, determines the rate of blood loss or bleeding time. One of the prior art blade-like puncturing devices developed for use in this test is shown in U.S. Pat. No. 4,078,552 to Chen et al.
Because the nerve endings in the finger tip area are quite sensitive, even such minimal skin punctures may be quite irritating and/or painful. In order to minimize the discomfort associated with such tests, it is desirable to make the puncture or penetration of the skin by the lancet as rapid and short-lived as possible. Moreover, in order to achieve some degree of standardization and repeatability as to the above-described bleeding time type of test, it is desirable that the lancet be designed so that the speed, effective time of penetration, and depth of penetration are standardized and repeatable from one lancet device to the next.
Various spring loaded lancets are known, some of which provide spring-loaded firing for standardization of the forces, velocities, and depth of penetration, and some of which provide spring-loaded, retractable features. For example, such spring-loaded and/or retractable lancets are shown in U.S. Pat. to Burns, Nos. 4,375,815 and 4,388,925 as well as in the U.S. Pat. to Burns No. et al, 4,449,529.
The retractable feature of some of these lancets is also desirable, in that it prevents reuse of the lancet, and requires disposal of the same after but one use. This is important for at least two reasons: firstly, for health and sanitary reasons it is inadvisable to reuse the same lancet on a second patient; and secondly, some technicians might reuse the blade of a preloaded or spring-loaded lancet after an initial firing thereof without restressing or preloading the spring, but rather by merely manually making the puncture, thus failing to take advantage of the preloaded, controlled force and velocity of the action thereof. In the second case, some of the prior art devices leave the cutting edge or point extended from the body or housing of the lancet after firing and may or may not permit reloading or recompression of the springs or other members which accomplish firing.
Some other lancets utilize a multiple spring arrangement, such as those shown in some of the Burns or Burns et al patents noted above. However, such assemblies are relatively complex and require a number of interfitting parts which are relatively difficult to manufacture and accurately assemble. Moreover, the use of two springs, one for firing of the lancet point or blade and a second for retracting the same after firing, presents a number of problems in accurately reproducing the tensile strengths and behavior, both in compression and upon release, of two oppositely acting springs. These factors can be difficult to uniformly reproduce in practice, at least in a relatively inexpensive, disposable product. This difficulty is due not only to the problems in selecting and properly mounting and pretensioning the springs themselves, but also in the difficulty of maintaining uniformity of housing or other casing parts within which the springs are mounted, maintaining accurate dimensions, controlling frictional forces, and the like.
In order to overcome the foregoing problems and address the foregoing considerations, we have devised a novel retractable, non-reusable bleeding time lancet apparatus. Our apparatus comprises a housing having an end opening, a blade, and a carrier for fixedly mounting the blade and mounted in the housing for sliding motion toward and away from the end opening. A resilient biasing member is mounted in the housing in a prestressed condition and is operatively coupled for selectively urging the carrier for achieving sliding motion toward and away from the housing end opening.
A non-resettable release member normally retains the biasing member in its prestressed condition and is selectively activatable for releasing the resilient biasing member to urge the carrier in a sliding motion for projecting at least a cutting edge of the blade through the end opening. Cooperating surfaces on the housing and carrier define respective limits of sliding motion of the carrier corresponding to extended and retracted positions of the blade cutting edge relative to the housing end opening.
The resilient biasing member is operatively engaged with the carrier for achieving a compound sliding movement of the carrier comprising an initial portion including extension of the carrier for projecting the blade cutting edge outwardly of the housing end opening, immediately followed by a second portion including retraction of the carrier for retraction of the blade cutting edge back into the housing.